Manufacture of foil seals

ABSTRACT

Molybdenum foils for pinch sealing into quartz are etched using shields which protect selected welding areas at each end from the action of the electrolyte. Etching provides feathered edges all around but leaves thicker areas under the shields to which the inleads and electrodes are welded without any need for extra tabs to facilitate welding or to increase the current carrying capacity. In a preferred foil-inlead construction, the inlead and electrode have spade ends coextensive with the thicker areas in the foils to which they are welded.

United States Patent Fridrich 51 Se t. 26, 1972 [54] MANUFACTURE OF FOILSEALS [72] Inventor: Elmer G. Fridrlch, 9933 Wilson Mills, Chardon, Ohio44024 [22] Filed: Aug. 27, 1970 [21] Appl. No.: 76,339

Related U.S. Application Data [62] Division of Ser. No. 734,910, June 6,1968,

Pat. No. 3,582,704.

[52] U.S. Cl ..29/475, 29/488 [51] Int. Cl. ..B23k 31/02 [58] Field ofSearch ..313/217, 331, 332; 29/488, 29/475 [56] References Cited UNITEDSTATES PATENTS 2,761,208 9/1956 Mitchell ..29/475 2,966,607 12/1960Thouret ..313/217 X 3,250,941 5/1966 Wilson et a1 ..313/217 X FOREIGNPATENTS OR APPLICATIONS 982,369 1/1951 France ..313/217 5/1961 Germany..313/332 8/1954 Great Britain ..313/331 Primary Examiner-John F.Campbell Assistant Examiner--Ronald .1. Shore Attorney-Ernest W. Legree,Henry P. Truesdell, Frank L. Neuhauser, Oscar B. Waddell and Melvin M.Goldenberg [5 7] ABSTRACT Molybdenum foils for pinch sealing into quartzare etched using shields which protect selected welding areas at eachend from the action of the electrolyte. Etching provides feathered edgesall around but leaves thicker areas under the shields to which theinleads and electrodes are welded without any need for extra tabs tofacilitate welding or to increase the current carrying capacity. In apreferred foil-inlead construction, the inlead and electrode have spadeends coextensive with the thicker areas in the foils to which they arewelded.

8 Claims, 7 Drawing Figures MANUFACTURE OF FOIL SEALS BACKGROUND OF THEINVENTION The invention relates to foil or ribbon seals into vitreousenvelopes of glass or quartz in lamp manufacturing. The high temperaturerequired for softening quartz restricts the choice of metals availablefor sealing through it in practice to molybdenum and tungsten, both ofwhich have coefficients of expansion much greater than quartz. To avoidcracking the quartz upon cooling, the conductor is shaped at least overthe hermetically sealing portion as a thin ribbon or foil. The foilportion goes into tension without rupturing when the quartz cools andcracking or shaling of the quartz is avoided.

For reliable sealing, a minimum ratio of about 100 to 1 between widthand thickness is necessary in the foil and in the thicker foils thereshould be a taper angle not exceeding about 5 to the edges. Foils havingsuch cross section can be obtained by rolling or etching. Longitudinallyrolled one piece molybdenum wire leads are described in U.S. Pat. No.2,667,595 Noel et al. and are particularly suitable for lower currents.For higher currents or where heavier electrodes have to be supported bythe foils during the sealing process, etched foils are preferred. Aninlead conductor is welded to one end of the etched foil and anelectrode or electrode support wire is welded to the other end.

SUMMARY OF THE INVENTION In welding conductors to thin foil, frequentlythe foil is burnt through and a defective weld results. Also the currentcarrying capacity of the combination is limited by that of the thin foilimmediately next to the weld. The object of the invention is to providea solution to these problems. 7

In accordance with my invention, etching ofthe foils is done in suchfashion as to leave a thicker region at each end of the foil to whichthe inlead and'the electrode conductors are welded. This mayconveniently be done by providing shielding means at each end of thefoil to protect the selected areas from the action of the electrolyte.Electrolytic etching in an alkali solution then provides feathered edgesall around but leaves thicker regions or plateaus under the clamps. Theinlead and the inner conductor which supports the electrode or energytranslation element such as a filament may readily be welded to thesethicker regions without any need for extra tabs to build up thethickness and facilitate welding or increase the current carryingcapacity.

In a preferred inlead-foil-electrode assembly for pinch-sealing into aquartz envelope, the inlead and electrode ends next the foil arespade-shaped and match the thicker areas in the foils to which they arewelded. This assures maximum strength and currentcarrying capacity, andavoids foil sections projecting laterally into the quartz next to thewelds which are too thick or insufficiently feathered to bond to thequartz.

DESCRIPTION OF DRAWING FIG. 1 shows in partly schematic form a set upfor electrolytic etching of foil according to the invention.

FIGS. 2a, b and c are respectively plan, longitudinal section, andtransverse section views of etched foil according to the invention withthe thickness shown exaggerated for ease of illustration. The sectionsare taken along the section lines conventionally indicated.

FIGS. 3a and b show a welded inlead-foil-electrode assembly in plan andside views respectively. I

FIG. 4 shows a complete discharge lamp with pinch seals utilizing etchedfoils in accordance with the invent1on.

DESCRIPTION OF PREFERRED EMBODIMENT AND PROCESS A pinch seal having acurrent capacity of 50 amperes utilizes as starting material amolybdenum foil 0.0065 inch thick by three-fourths inch wide by 1 inchlong. In accordance with the invention, the foil is electrolyticallyetched to provide feathered edges all around and thicker welding areasat both ends. This may be done in the apparatus illustrated in FIG. 1.Tl-le foil 1 is inserted between the legs of a springy metal clamp orholder 2 whose lower extremities are covered with thick insulating bootsor shields 3 of flexible and resilient plastic material, suitablypolyethylene. The plastic shields are slit on the inside near theirlower extremities so as to permit penetration by the molybdenum foil upto contact of the clamp by the edge of the foil. The plastic shieldsprotect the portions of the foil which penetrates into the slits and theends of the clamp 2 from the action of the electrolyte. The otherelectrode consists of a ring-shaped copper band 4 which is supported bya copper conductor 5 to which electrical connections are made. Themolybdenum foil 1 and the ring electrode 4 are supported in the sameplane in a basin '6 which is filled with the electrolyte, suitably a 20percent solution of sodium hydroxide:

The use of alternating current for etching is preferred and a current of25 to 50 amperes is suitable for the size of foil illustrated. Etchingis most rapid at the edges and is a maximum at the corners of the foil.This causes the comers to become rounded and the edges to becomefeathered as illustrated in FIGS. 2a and 20. However etching takes placeall over except in the areas inserted into the shields 3 where theelectrolyte does not have access to the foil. This results in thickerareas or plateaus 8,9 at both ends of the foil which remain at theoriginal thickness of 0.0065 inch. From the thicker areas, the thicknesstapers gradually to that of the foil. Along the medial line of the foil,the thickness in the central part may be approximately half what it isat the thicker areas, as illustrated in FIG. 2b. Where the originalthickness was 0.0065 inch, the thickness along the medial line afteretching may be 0.0035 inch. The thickness tapers substantially to zeroat the edges, except at the shoulders 10 of the thicker areas 8,9 wherethe original foil thickness remains unchanged.

The etching process according to the invention results in a taper inthickness in the merging regions 8',9' up to the welding plateaus 8,9which increases the current carrying capacity. In foils not having thisfeature, it is in the region immediately around the weld points thatexcessive heating takes place and sets the limit on the current carryingcapacity of the foil. The tapering in thickness up to the weldingplateaus in the foils prepared in accordance with my invention meansthat the limit in current capacity is set by the overall heating of thefoil. Overall heating is determined by the cross sectional area so thatthe current carrying capacity is increased severalfold.

FIGS. 3a and b illustrate an inlead assembly utilizing the etchedmolybdenum foil 1 of the invention extending between a rod-likemolybdenum inlead conductor 11 and a rod-like tungsten electrode 12.Both the inlead and electrode are spread or flattened at 11a, 12a,suitably by not swaging, resulting in spade-shaped ends next to thefoils. The spade-ends match the thicker areas 8,9 projecting at the endsof the foils and they are substantially coextensive in area. Thus afterwelding there are no sections of foil projecting laterally from the weldregions as at the shoulders 10 which are unetched or unfeathered andwhich would not bond properly and would cause weakness in the quartz.

To facilitate welding, the spade ends and thicker regions in the foilare first coated with a slurry of tungsten, molybdenum, and rheniumpowders and fired in hydrogen. The parts are then pressed together andelectric-welded. The thickness of the spade-ends is not critical becausethey do not seal to the quartz and 0.010 inch is convenient. ln FIGS.2b, 2c and 3b the thickness of the foil has been greatly exaggerated topermit illustration. The combination of spade ends on the inlead andelectrode matching the thicker nonetched regions in the foils achievesmaximum strength current-carrying current capacity. At the same time,weakness in the quartz from laterally projecting unfeathered sectionswhich are incapable of bonding is avoided.

FIG. 4 illustrates a high-intensity compact source lamp 13 comprising athick-walled quartz envelope 14 containing an ionizable filling such asindium iodide. Etched foil inlead assemblies made according to thepresent invention are pinched-sealed at 15 and 16 into the ends of theenvelope and support anode and cathode l7 and 18 respectively. The useof etched foils according to the invention in the dimensions previouslystated permits currents up to 50 amperes without overheating the seals.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of making foil-conductor assemblies for sealing intovitreous material which comprises electrolytically etching a refractorymetal foil while shielding an area at each end of the foil from theelectrolyte in order to provide feathered edges all around and thickerareas at the ends which taper gradually to the thickness of the foil,and welding conductors to said thickened areas.

2. The method of claim 1 wherein conductors having flattened endsmatching said thicker areas are welded co-extensively with said thickerareas.

3. The method of claim 1 wherein said metal foil is molybdenum.

4. The method of claim 2 wherein said metal foil is molybdenum.

5. The method of making a foil-conductor assembly for sealin intovitreou ma erial which 0 rises:

contacFlng an end of a reiractory metaT f oi I by an end portion of aconductor covered by a boot of flexible resilient insulating materialhaving a slit therein for accommodating said foil, said slit determininga shielded portion of said foil;

placing said foil and the end portion of said conductor in anelectrolyte and passing current therethrough to etch the surface of saidfoil except for the shielded portion whereby said shielded portionremains undiminished in thickness and tapers to the thickness of theremainder of the foil which acquires feathered edges; and

welding a conductor to said shielded portion.

6. The method of claim 5 wherein each end of said foil is contacted byan end portion of a conductor covered by a boot of flexible resilientinsulating materia1 having a slit therein accommodating an end of saidfoil whereby, after etching, a shielded portion of undiminishedthickness is left at each end of said foil; and welding a conductor toeach shielded portion.

7. The method of claim 5 wherein said metal foil is molybdenum.

8. The method of claim 6 wherein said metal foil is molybdenum.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORECTION Paten No. 3.693 241Dated September 26 1972 lnventofls) Elmer G. Fr'idrich It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover sheet insert [73] Assignee General Electric Company, acorporation of New York Signed and sealed this 1st day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of PatentsAttesting Officer USCOMM-DC 60376-1 69 "WM P O-1050 (IO-69) Q u.s.GOVERNMENT PRINTING OFFICE I959 o-ass-au,

2. The method of claim 1 wherein conductors having flattened endsmatching said thicker areas are welded co-extensively with said thickerareas.
 3. The method of claim 1 wherein said metal foil is molybdenum.4. The method of claim 2 wherein said metal foil is molybdenum.
 5. Themethod of making a foil-conductor assembly for sealing into vitreousmaterial which comprises: contacting an end of a refractory metal foilby an end portion of a conductor covered by a boot of flexible resilientinsulating material having a slit therein for accommodating said foil,said slit determining a shielded portion of said foil; placing said foiland the end portion of said conductor in an electrolyte and passingcurrent therethrough to etch the surface of said foil except for theshielded portion whereby said shielded portion remains undiminished inthickness and tapers to the thickness of the remainder of the foil whichacquires feathered edges; and welding a conductor to said shieldedportion.
 6. The method of claim 5 wherein each end of said foil iscontacted by an end portion of a conductor covered by a boot of flexibleresilient insulating material having a slit therein accommodating an endof said foil whereby, after etching, a shielded portion of undiminishedthickness is left at each end of said foil; and welding a conductor toeach shielded portion.
 7. The method of claim 5 wherein said metal foilis molybdenum.
 8. The method of claim 6 wherein said metal foil ismolybdenum.